The present invention relates to a display device, or particularly to a flat type display device which uses an anisotropic conductive film for connection with a driver circuit.
Flat display panels such as LCD (liquid crystal display), ECD (electrochromic display), EL (electro luminescence) and PDP (plasma display panel) (hereinafter referred to as display panels) have electrodes with multiple terminals. Tape automated bonding (TAB) is one of the applicable techniques for mounting an LSI driver for driving a display device with multi-terminal electrodes. Normally, the LSI driver is mounted on a tape carrier by inner lead bonding (ILB), and an anisotropic conductive film is temporarily applied by pressure to the tape carrier on the surface to be in contact with the display panel. The tape carrier, which has the LSI driver is mounted therein, is positioned on the display panel and connected to the display panel under heat pressure.
Hereinafter, the anisotropic conductive film will be described in detail. As shown in FIG. 5, the conventional anisotropic conductive resin tape for heat pressure connection contains conductive particles 102' such as Ag, Ni and Cu in powder form and carbon fibers in a resin tape 101'. The resin tape 101' which is clamped under a certain pressure between the terminals 104 on a PC board 103, for example, and the terminal 106 on a glass substrate 105 is heated. Then the adhesive property of the resin permits a firm connection between the PC board 103 and the glass substrate 105. The conductive particles 102' existing between the terminals 104 and 106 effects the electrical connection between the board 103 and the substrate 105. This type of anisotropic conductive film is disclosed in the U.S. Pat. No. 4,113,981. The anisotropic conductive film having conductive particles 102' which are elastic is disclosed in the U.S. Pat. No. 4,680,226.
The method of electrically connecting the LSI driver mounted on a tape carrier to the terminals of a display panel using the anisotropic conductive film is described as follows with reference to FIGS. 6 and 7.
The tape carrier includes electrodes 203 and 204 formed on a base material 201. The LSI driver 202 is mounted by ILB in the center of the tape carrier. The output of the LSI 202 is led to the cut end 206 of the tape carrier, and the input is led in the opposite direction. The output portion serves as an area 205 for connection with a display panel 207. The anisotropic conductive film 208 is temporarily applied by pressure to this contact area 205, and then the tape carrier is connected to the display panel 207 by heating under pressure.
With the tape carrier of the above construction, however, when the anisotropic conductive film 208 is heated under pressure, the film may extend to the region between the electrodes and to the areas 209 and 210 outside the contact area 205. If metal particles in the anisotropic conductive film 208 extend to the areas 209 and 210 between the electrodes, a conducting path is formed by the metal particles, which causes electrical leakage and/or short circuits.